This is a 12-week, intent-to-treat, randomized controlled trial to evaluate the impact of N-Acetylcysteine (NAC) versus matched placebo (PBO) twice daily, added to compliance enhancement (CE) and contingency management (CM) interventions, on cannabis use among treatment-seeking adults. The primary analysis will evaluate the impact of NAC versus PBO on cannabis use during the 12-week treatment intervention with the primary outcome measure being the proportion of negative urine cannabinoid tests submitted during active treatment, compared between the two treatment groups.